The present invention relates to the field of safety devices for industrial machinery, and particularly to light curtains used as safety devices for robotic machines.
Industrial machines which incorporate robotic movement present a safety concern when humans are required to work near the moving machinery. Should a human working near the machine become careless and come into direct contact with the moving machinery, a serious accident may occur, resulting in the loss of human life or limb. To reduce the risk of such injury, many machines utilize safety devices which block humans from coming into contact with moving machinery. These safety devices often take the form of physical enclosures, such as plexiglass walls, which completely block the entry of objects into the machine's working space defined by the physical enclosure. While these physical enclosures properly prevent the entry of foreign objects into the machine's working space, there are several disadvantages to such physical enclosures. First, physical enclosures add substantially to the total cost of the robotic machine because of additional engineering time required to design an effective enclosure and additional materials required to build the physical enclosures. Next, physical enclosures often impede the vision of human operators into the working space of the machine. For example, even if a transparent plexiglass is used for a portion of the physical enclosure, the plexiglass may become scratched or clouded, or a glare may reflect from the plexiglass, thus impeding vision. Further, physical enclosures prevent entry of a human or a robot into the machine working space, when required. For example, a robot or human may need to enter the working space at a particular time to load parts within the machine working space. Also, if the machine is in need of repair, it is desirable for a human to have quick and easy access to the working space of the machine in order to make the repair. For these reasons, light curtain safety systems are often preferred to physical enclosures because light curtains provide a protective barrier while still allowing for clear vision into the machine working space and also allowing for quick and easy access to the machine working space when required.
Light curtains generally comprise light emitting diodes (LEDs) which direct streams of light to light detectors positioned directly opposite each LED. Light stretching from one LED to its opposing light detector may be considered a single "bar of light". If the LEDs are arranged in a row, multiple bars of light are formed within a single plane to form an invisible barrier or "light curtain". Alternatively, some light curtains use a reflective member opposite the LED to direct the bar of light to a detector positioned somewhere other than opposite the LED, such as next to the LED. When an object comes into contact with the light curtain, at least one of the bars of light is broken, and the detector associated with the broken bar of light sends a signal that the light curtain has been breached. When the machinery receives a breach signal, an alarm is triggered, and the machinery protected by the light curtain is immediately stopped. In this manner, the light curtain prevents injury to humans who accidentally breach the light curtain and enter the working space of the machine. At the same time, light curtains allow for unimpaired vision and easy access to the working space of a robotic machine.
While light curtains provide an improved safety mechanism for preventing injury, several problems remain with the use of light curtains as safety devices for robotic machines. First, light curtains may be as costly, if not more costly to design and build than physical enclosures. In order to form a "bar of light", operational elements such as LEDs, detectors, and reflective devices must be positioned on at least two sides of the light curtain. Supporting structures are also required on at least two sides of the light curtain to support the operational elements. A large cost of designing and producing a light curtain could be removed if a light curtain could be formed with operational elements and supporting structures on only one side of the light curtain.
Another problem with typical light curtains is that entry into any part of the working space of the robotic machine, as defined by the light curtain, is absolutely prohibited during operation of the machine. In many situations, it may be useful for the operator to actually enter into a particular region of the machine working space while the machine is operating. For example, it would be useful for an operator to be allowed to enter a first working area of a robotic machine to load a part on a platform while the machine works in a second area, but to be restricted from the first area as a robot approaches the platform to manipulate the part on the platform.